The hydroformylation of an olefinic compound with carbon monoxide and hydrogen to produce aldehydes using an organic solubilized transition metal-phosphorus ligand complex catalyst is well known in the art.
It is further well known that the phosphorus ligand employed in such catalyzed hydroformylation processes may have a direct effect on the success of such a given process. Moreover, the selection of the particular phosphorus ligand to be used in any such transition metal catalyzed hydroformylation process depends in the main on the end result desired, since the best overall processing efficiency may require a compromise between numerous factors involved. For example, in hydroformylation such factors as aldehyde product selectivity (i.e., normal to branched chain aldehyde product ratios), catalyst reactivity and stability, and ligand stability are often of major concern in the selection of the desired phosphorus ligand to be employed. For instance, U.S. Pat. No. 3,527,809 teaches how alpha olefins can be selectively hydroformylated with rhodium-triorganophosphine or triorganophosphite ligand complexes to produce oxygenated products rich in normal aldehydes, while U.S. Pat. Nos. 4,148,830 and 4,247,486 disclose both liquid and gas recycle operations directed to the same result using a rhodium triarylphosphine ligand complex catalyst. U.S. Pat. No. 4,283,562 discloses that branched-alkylphenylphosphine or cycloalkylphenylphosphine ligands can be employed in a rhodium catalyzed hydroformylation process in order to provide a more stable catalyst against intrinsic deactivation. U.S. Pat. No. 4,400,548 discloses that bisphosphine monoxide ligands can be employed to provide rhodium complex catalysts of improved thermal stability useful for the hydroformylation production of aldehydes.
However, despite the obvious benefits attendant with the prior art references mentioned above, the search continues for phosphorus ligands which will more effectively satisfy additional ligand requirements, particularly with regard to ligand volatility.
For example, rhodium complex catalyzed hydroformylation processes are preferably carried out in a non-aqueous hydroformylation reaction medium containing both the soluble catalyst complex and free excess phosphorus ligand, i.e., ligand not tied to or bound to the rhodium complex. In such processes the desired aldehyde product is preferably separated and recovered from the reaction product medium by distillation, and in the case of continuous liquid catalyst recycle operations, the non volatilized catalyst ligand containing residue is recycled to the reactor. Accordingly, an important requirement of such processes is the effective separation and recovery of the desired aldehyde product from its hydroformylation reaction product medium without excessive phosphorus ligand and/or catalyst complex loss. Thus in such non-aqueous hydroformylation processes, and in particular liquid catalyst recycle processes, the volatility of the phosphorus ligand is also of primary concern, since continuous removal (stripping) of the phosphorus ligand during aldehyde product separation via distillation can result not only in high phosphorus ligand loss which must be replaced, but can also lead to changes in the catalyst properties and even eventual catalyst deactivation. Indeed, if the rate of such simultaneous volatilization of the phosphorus ligand is too high an additional ligand recovery/recycle scheme may be required in order for the process to be economical.
While, this problem of ligand volatility (re aldehyde product separation) in non aqueous hydroformylation may not be as overwhelming when low molecular weight olefins, such as propylene, are hydroformylated, using conventional tertiary phosphines such as triphenylphosphine, it is still of some concern and said problem increases and magnifies when the process is directed to the hydroformylation of long chain olefinic compounds (e.g., C.sub.6 to C.sub.20 alpha-olefins) to produce their corresponding higher molecular weight aldehydes due to the high temperatures necessary to volatilize such high molecular weight aldehyde products from the hydroformylation reaction product medium. Likewise ligand loss due to volatility, when higher boiling aldehyde condensation by products, such as trimers, etc., are desired to be removed e.g. from catalyst containing hydroformylation residues, in order to recover such catalysts and ligands is also of major concern to the art regardless of whether or not such aldehyde condensation by products are the result of hydroformylating low (e.g. C.sub.2 -C.sub.5) or high (e.g. C.sub.6 -C.sub.20) molecular weight olefins.
It has been proposed to use aqueous solutions of sulfonated aryl phosphine compounds as the phosphorus ligand, such as the sulfonated triphenylphosphine salts disclosed e.g., in EPC No. 163234 and U.S. Pat. Nos. 4,248,802, 4,399,312, and the like, as the phosphorus ligand in the hydroformylation process to facilitate the separation and recovery of the rhodium complex catalyst. However, all such prior art methods also involve the employment of an aqueous hydroformylation reaction medium made up of both an organic phase containing the reaction starting materials and/or products and an aqueous or water phase containing the catalyst complex and sulfonated phosphine ligands, in contrast to a non-aqueous hydroformylation reaction medium. Moreover, such aqueous or water phase type hydroformylation systems in general require high reactor pressures and/or high rhodium concentrations and may also require buffers or phase transfer reagents and/or the use of larger and more costly processing apparatus equipment.
Therefore there is a definite need in the hydroformylation art for low volatile/organic soluble phosphorus ligands which will function effectively in a non-aqueous rhodium catalyzed hydroformylation process with regard to hydroformylating both low molecular weight olefins (e.g., C.sub.2 to C.sub.5 olefins) and in particular long chain, high molecular weight olefinic compounds, (e.g., C.sub.6 to C.sub.20 olefins).